This page explains how to start and complete the Secret of the Cedars shrine quest.
How to Start the Quest
Talk to Clavia at Hateno Village to start the quest. She can be found on the dock behind Kochi Dye Shop or in her house (the Village Chief's house, which is just west of the inn).
How to Complete the Quest
Check the Tahno O'ah Shrine page for details on completing the quest.